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Edwin Hubble

[huhb-uhl]

Edwin Powell Hubble (November 20, 1889September 28, 1953) was an American astronomer. He profoundly changed astronomers' understanding of the nature of the universe by demonstrating the existence of other galaxies besides the Milky Way. He also discovered that the degree of redshift observed in light coming from a galaxy increased in proportion to the distance of that galaxy from the Milky Way. This became known as Hubble's law, and would help establish that the universe is expanding.

Biography

He was born to an insurance executive in Marshfield, Missouri and moved to Wheaton, Illinois in 1889. In his younger days he was noted more for his athletic prowess than his intellectual abilities, although he did earn good grades in every subject except for spelling. He won seven first places and a third place in a single high school track meet in 1906. That year he also set a state record for high jump in Illinois.

His studies at the University of Chicago concentrated on mathematics, astronomy, and philosophy which led to a BS degree in 1910. Hubble also became a member of the Kappa Sigma Fraternity and in 1948 was named Kappa Sigma "Man of the Year". He spent the next three years as one of Oxford's first Rhodes Scholars, where he originally studied jurisprudence, before switching his major to Spanish and receiving the MA degree, after which he returned to the United States. Some of his British mannerisms and dress stayed with him all his life, occasionally irritating his American colleagues.

Returning to the United States he worked as a high school teacher and a basketball coach at New Albany High School in New Albany, Indiana (near Louisville, Kentucky), and was a member of the Kentucky bar, although he reportedly never actually practiced law in Kentucky. He served in World War I and quickly advanced to the rank of major. He returned to astronomy at the Yerkes Observatory of the University of Chicago, where he earned a PhD in 1917 with a dissertation entitled Photographic Investigations of Faint Nebulae

In 1919 Hubble was offered a staff position by George Ellery Hale, the founder and director of Carnegie Institution's Mount Wilson Observatory, near Pasadena, California, where he remained until his death. He also served in the US Army at the Aberdeen Proving Ground during World War II. For his work there he received the Legion of Merit. Shortly before his death, Palomar's 200-inch Hale Telescope was completed; Hubble was the first to use it. Hubble continued his researches at the Mount Wilson and Palomar Observatories, where he remained active until his death.

Hubble died of a cerebral thrombosis on September 28, 1953, in San Marino, California. No funeral was held and his wife, Grace, did not reveal what happened to his body.

Discoveries

The Universe goes beyond the Milky Way galaxy

Hubble's arrival at Mount Wilson in 1919 coincided roughly with the completion of the 100-inch Hooker Telescope, then the world's largest telescope. At that time, the prevailing view of the cosmos was that the universe consisted entirely of the Milky Way. Using the Hooker Telescope, Hubble identified Cepheid variables (a kind of star; see also standard candle) in several spiral nebulae, including the Andromeda Galaxy. His observations, made in 1922–1923, proved conclusively that these nebulae were much too distant to be part of the Milky Way and were, in fact, entire galaxies outside our own. This idea had been opposed by many in the astronomy establishment of the time, in particular by Harvard-based Harlow Shapley. Hubble's discovery, announced on January 1, 1925, fundamentally changed the view of the universe.

Hubble also devised the most commonly used system for classifying galaxies, grouping them according to their appearance in photographic images. He arranged the different groups of galaxies in what became known as the Hubble sequence.

Redshift increases with distance

Hubble was generally incorrectly credited with discovering the redshift of galaxies. These measurements and their significance were understood before 1918 by James Edward Keeler (Lick & Allegheny), Vesto Melvin Slipher (Lowell), and Professor William Wallace Campbell (Lick) at other observatories. Combining his own measurements of galaxy distances with Vesto Slipher's measurements of the redshifts associated with the galaxies, Hubble and Milton L. Humason discovered a rough proportionality of the objects' distances with their redshifts. Though there was considerable scatter (now known to be due to peculiar velocities), Hubble and Humason were able to plot a trend line from the 46 galaxies they studied and obtained a value for the Hubble-Humason constant of 500 km/s/Mpc, which is much higher than the currently accepted value due to errors in their distance calibrations. In 1929 Hubble and Humason formulated the empirical Redshift Distance Law of galaxies, nowadays termed simply Hubble's law, which, if the redshift is interpreted as a measure of recession speed, is consistent with the solutions of Einstein’s equations of general relativity for a homogeneous, isotropic expanding space. Although concepts underlying an expanding universe were well understood earlier, this statement by Hubble and Humason led to wider scale acceptance for this view. The law states that the greater the distance between any two galaxies, the greater their relative speed of separation.

This discovery was the first observational support for the Big Bang theory which had been proposed by Alexander Friedmann in 1922. The observed velocities of distant galaxies, taken together with the cosmological principle appeared to show that the Universe was expanding in a manner consistent with the Friedmann-Lemaître model of general relativity. In 1931 Hubble wrote a letter to the Dutch cosmologist Willem De Sitter expressing his opinion on the theoretical interpretation of the redshift-distance relation:

"... we use the term 'apparent velocities' in order to emphasize the empirical feature of the correlation. The interpretation, we feel, should be left to you and the very few others who are competent to discuss the matter with authority."
Today, the 'apparent velocities' in question are considered to be artifacts of a coordinate transformation that occurs in an expanding space. Light traveling through stretching space will experience a Hubble-type redshift, a mechanism different from the Doppler effect.

In the 1930s Hubble was involved in determining the distribution of galaxies and spatial curvature. These data seemed to indicate that the universe was flat and homogeneous, but there was a deviation from flatness at large redshifts. According to Allan Sandage,

"Hubble believed that his count data gave a more reasonable result concerning spatial curvature if the redshift correction was made assuming no recession. To the very end of his writings he maintained this position, favouring (or at the very least keeping open) the model where no true expansion exists, and therefore that the redshift "represents a hitherto unrecognized principle of nature.
There were methodological problems with Hubble's survey technique that showed a deviation from flatness at large redshifts. In particular the technique did not account for changes in luminosity of galaxies due to galaxy evolution.

Earlier, in 1917, Albert Einstein had found that his newly developed theory of general relativity indicated that the universe must be either expanding or contracting. Unable to believe what his own equations were telling him, Einstein introduced a cosmological constant (a "fudge factor") to the equations to avoid this "problem". When Einstein heard of Hubble's discovery, he said that changing his equations was "the biggest blunder of [his] life".

Other discoveries

Hubble discovered the asteroid 1373 Cincinnati on August 30, 1935. He also wrote The Observational Approach to Cosmology and The Realm of the Nebulae around this time.

Nobel Prize

Hubble spent much of the later part of his career attempting to have astronomy considered an area of physics, instead of being its own science. He did this largely so that astronomers - including himself - could be recognized by the Nobel Prize Committee for their valuable contributions to astrophysics. This campaign was unsuccessful in Hubble's lifetime, but shortly after his death the Nobel Prize Committee decided that astronomical work would be eligible for the physics prize.

On March 6, 2008, the United States Postal Service released a 41 cent stamp honoring Hubble on a sheet titled "American Scientists." His citation reads: 'Often called a "pioneer of the distant stars," astronomer Edwin Hubble (1889-1953) played a pivotal role in deciphering the vast and complex nature of the universe. His meticulous studies of spiral nebulae proved the existence of galaxies other than our own Milky Way. Had he not died suddenly in 1953, Hubble would have won that year's Nobel Prize in Physics.' The other scientists on the "American Scientists" sheet include Gerty Cori, biochemist; Linus Pauling, chemist; and John Bardeen, physicist.

Honors

Awards

Named after him

Notes

References

See also

External links

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